First, you must consider adding insulation to the walls, because about 40% of the heat is lost through them; roof insulation comes in second place, in order to prevent about 25% of heat loss. Before adding insulation, there are some things to consider:

· providing enough fresh air through adequate ventilation or controlled infiltration (if you add too much insulation on a tight home, you risk to leave its occupants without enough fresh air, which may cause respiratory problems and allergies)

· sealing all uncontrolled air leaks (failing to do this will make insulation to lose its main purpose)

· preventing moisture accumulation, by using vapor retarders as well as adequate ventilation of the house

There are specific R-levels recommended according to the climate in each area. When it comes to Illinois, we are talking about 13 R-value for existing walls, 21 for new walls, 43 for the attic, 21 for the floor over unconditioned space and 10 for basement walls.

These levels must be compared with typical R-values of different insulating materials. Not least, before determining how much insulation you need, you must determine how much insulation you already have.